This invention relates generally to measuring instruments. More particularly, this invention relates to a protractor that permits a user to quickly and easily describe and define a wide variety of angular measurements.
Protractors are well known and are used in a variety of fields and industries. For example, protractors are often used by school children who are learning how to define and a describe angular measures and to draw lines, shapes and figures that incorporate these measurements.
A typical prior art protractor 10 is shown in FIG. 1A. The prior art protractor 10 includes a horizontal member 12 coupled to a semi-circular member 14 that substantially circumscribes one side of the horizontal member 12. At the center of the horizontal member 12 is a center marking 16 which is used as a starting point for angular measurements. Along the outer edge 23 of the semi-circular member 14 are a plurality of radial markings 18 that are used to indicate the size, in degrees, of the particular angle relative to zero line 20 of the horizontal member 12.
Although such prior art protractors are useful, they have a number of shortcomings. For example, users in general, and particularly children, often wish to not only determine the magnitude of certain angles, but also wish to draw lines that will describe or define those angles. In the case of the prior art protractor shown in FIG. 1A the zero degree line 20 is offset from the inner edge 25 of the horizontal member 12 preventing the user from drawing one of the two lines necessary to describe an angle. Additionally, there is no second straight edge that can be used to describe the second line. For this reason, the user must use a second instrument, such as a ruler, to describe these lines. Because multiple instruments are required for this task, however, the accuracy of any angular definition can be diminished during the removal and/or placement of the instruments to be used in describing the angle. Additionally, the prior art protractor 10 shown in FIG. 1 typically has a very flat surface which can be especially difficult to grip and keep in a fixed position when making an angular measurement. This can be an especially difficult problem for young children, who have smaller hands and less developed coordination than an average adult.
A second prior art protractor is shown in FIG. 1B. The second prior art protractor 110 includes horizontal and semi-circular members 112 and 114 respectively, in a similar arrangement as shown in FIG. 1A. Similarly, the second prior art protractor 110 includes a center marking 116 and radial markings 118 along the outer edge 123 of the semi-circular member 114. The second prior art protractor 110 also includes a lever arm 125 that rotates about the center marking 116 via a pin-hole combination 127. The lever arm 125 serves as a guide that allows a user to more accurately define the angle being measured.
This arrangement also has disadvantages, however. For example, due to the pin-hole combination 127 of the second prior art protractor 110, the protractor 110 must have a zero line 120 that is offset from the inner edge 129 of the horizontal member 112. Because the zero-degree line is offset, a user cannot draw a complete and unbroken zero line without moving the protractor 110. Additionally, because the center marking 116 is offset from the inner edge 129 of the horizontal member 112, the user is unable to draw a second line along the lever arm 125 to the center marking 116 without moving the protractor.
It is therefore an object of the invention to provide a protractor that permits a user to define and describe a variety of angles and the starting and ending edges thereof with a single instrument.
It is a further object of this invention to provide an improved protractor that permits a user to accurately define a variety of angular measurements.
It is yet another object of this invention to provide a novel protractor that can easily be gripped by a user without affecting the accuracy of any angular measurements being made.
It is still another object of the invention to provide a novel protractor that enables a user to draw a complete angle and the point where the two outer lines of the angle intersect, wherein the corner created by the intersection of the two lines is always visible and accessible.
In accordance with these objects of the invention, an improved protractor is provided comprising a frame and an arm. The frame includes a first substantially straight edge and a circular track which is engaged with a concentric channel located on one side of the arm. The arm also includes at least one straight edge which is used to define one of the two boundaries of an angle. The combination of the track and channel permit the user to rotate the arm about an axis that is substantially orthogonal to both the arm and the frame, allowing the user to define a variety of angles between the edges on the frame and the arm. The arm is also provided with a gripping surface that allows the user to hold the protractor without affecting the measurement of the appropriate angle.
These and other objects, advantages and features of the invention, together with the organization and manner of operation thereof, will become apparent from the following detailed description when taken in conjunction with the accompanying drawings, wherein like elements have like numerals throughout the drawings described below.